A bomb hidden in an ambulance has killed at least 95 people and injured more than 150 in the heavily fortified heart of the Afghan capital, Kabul, in the latest in a string of high-profile attacks.

The suicide bomber struck at a police checkpoint where the streets were crowded with people queueing to visit nearby offices and embassies, and vendors serving them. Witnesses said bodies were strewn across the pavement.

“It’s a massacre,” said Dejan Panic, a coordinator for the nearby emergency hospital, which was nearly overwhelmed by the flood of victims. Dozens were laid out on mattresses in the courtyard to wait for treatment from medics with the Italian charity, which was still tending to patients from previous attacks.

The bombing was the deadliest in Kabul for nearly eight months, a warning that even though the US has stepped up operations against insurgents, they still have the capacity to carry out attacks in government strongholds.

This week alone shut down a charity that serves millions of Afghans by targeting its headquarters, and a Taliban attack on a high-profile hotel and providing vital transport links over militant-controlled territory.

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Although US air power and other military support mean insurgents would struggle to mount a direct attack on Kabul, each attack undermines government efforts to create even a limited, protected version of normality.

The Taliban claimed the attack, naming the bomber as Salahuddin from southern Kandahar province. Spokesman Zabiullah Mujahid said the blast had killed only police officers, but witnesses described the dead as mostly civilians.

“Many women and children have been killed or wounded, because they were queuing outside the passport department,” said Sediqullah Popalzai, a national security official who was near the bomb when it detonated.

“Dead bodies which were near the ambulance were unidentifiable. There were shattered bodies everywhere. It was a very tragic and devastating scene.”

Some interior ministry offices and the EU, Dutch and Swedish embassies are on the street that was targeted, but they are heavily fortified and likely to have sustained only limited damage.

The attacker passed a first checkpoint by claiming he was rushing a patient to a nearby hospital, officials said, and then detonated his bomb when he was stopped at a second checkpoint.

The branch of the International Committee of the Red Cross (ICRC) warned that the bomber’s “harrowing” use of an ambulance could break international law.

“This could amount to perfidy under IHL (). Unacceptable and unjustifiable,” the group said on Twitter.

ICRC (@ICRC)

A tragic and senseless attack.

Ambulances are for saving lives, not destroying them.

As ambulances raced to collect the injured, nervous security forces also had to watch out for possible secondary attacks, and the nature of the first attack meant even medical teams were suspect. Popalzai said he had seen police stop one ambulance, and arrest three people inside.

The streets were busy when the bomber struck. As well as the embassies and offices, the checkpoint he targeted is near a popular street of carpet and handicraft shops and a major road. After the explosion all were crammed with injured and terrified survivors desperate to escape.

“It was the city of fear, everyone was running,” said Niloofar Ibrahimi who was working in a nearby bank when the blast hit. “Some people were crying because they lost a loved one and some were crying because they had no news about their loved ones.”

The attack came a week after Taliban attackers , killing at least 22 people, and four days after an Isis suicide bomber charity in eastern Afghanistan.

It raises serious questions about security, more than three years after then US president Barack Obama .

After the Taliban and Isis made inroads around the country, repeatedly threatening and occasionally overrunning provincial capitals, the US stepped up support for Afghan forces and increased airstrikes.

The officer in charge of the mission, Gen John Nicholson, described the greater US role as a “gamechanger”, and said Afghanistan had in its long fight against extremists.

But the recent assaults show insurgents are still capable of complex attacks that are damaging to both morale and infrastructure. And they come in winter, when the Taliban have traditionally retreated to havens in Pakistan, waiting for the summer fighting season.

“The Taliban has demonstrated repeatedly that it can stage mass-casualty attacks in urban spaces, and seemingly at will. To me, that’s a sign of strength, not weakness,” said Michael Kugelman, a senior analyst for south Asia at the Wilson Center in Washington DC.